1. Field of the Invention
The present invention relates to a two-channel, four loudspeaker-component enhanced stereophonic system, and more particularly to a stereophonic system having enclosures in each of which a front loudspeaker system and a rear loudspeaker system are placed and two electronic matrix networks which utilize two-channel information in driving each of the two rear loudspeaker systems.
2. Description of the Prior Art
U.S. Pat. No. 3,697,692, entitled Two-Channel, Four Component Stereophonic System, issued to David Hafler on Oct. 10, 1972, teaches a two-channel, four-component stereophonic system into which a two-channel stereo signal including left and right channel responses (L and R, respectively) derived from only two amplifiers is fed. The stereophonic system includes four speakers which are located approximately at the corners of a quadrilateral area and which are positioned so that each of them faces toward the interior of the area. An electronic network drives the four loudspeaker systems with four different signals, which have been derived from the original left and right channels, so that the sound from the loudspeaker systems appears to the listener, who is positioned interiorly of the area, to come from the four sides of the area rather than the four corners. The loudspeaker systems in the left and right front corners respond to (L+R/2) and (R+L/2), respectively, while in the left and right rear corners the loudspeaker systems respond to (L-R/2) and (R-L/2), respectively.
U.S. Pat. No. 4,191,852, entitled Stereophonic Sense Enhancing Apparatus, issued to Masao Nishikawa on Mar. 4, 1980, teaches an apparatus for effectively increasing stereophonic sense when the distance between the left and right loudspeakers is small. The apparatus enlarges the apparent distance between the left and right sources of sound by vectorially adding the sound signals of the left and right channels. The apparatus has a phase reversing circuit, a mixer circuit, and a band-pass filter in each of the left and the right channels. The phase reversing circuit is a negative feedback type tone control circuit. The mixer circuit includes a stereophonic sense increasing effect on-off switch device which is capable of switching load impedances. The band-pass filter passes a sound frequency band that is useful for increasing the stereophonic sense.
U.S. Pat. Nos. 3,164,676, 3,637,938 and 3,632,886 all teach enhanced stereophonic systems. All of the above enhanced stereophonic systems have their front and rear loudspeaker systems mounted in separate enclosures each of which is placed in separate positions in the room. It would be far more convenient, as well as sonically more accurate, to place each set of front and rear loudspeaker systems in a single enclosure with the front loudspeaker system mounted in such a way as to face the listener, and the rear loudspeaker system mounted in such a way as to face the wall behind the enclosure, and with the electronic matrix networks converting both left and right channel amplifier signals into each of the two new rear channel signals for the purpose of driving the rear loudspeaker systems. It would also be sonically more accurate to apply the left and right channel amplifier signals directly to the left and right front loudspeaker systems, respectively. It should be noted that stereophonic systems have been built and marketed which have separate rear-facing loudspeaker systems. However, these stereophonic systems do not have any electronic matrix type networks driving the rear loudspeaker systems.
One of the problems confronted with a front loudspeaker system and a rear loudspeaker system mounted in the same enclosure and in which the rear loudspeaker system is driven by an electronic matrix network is that sound energy of lower frequencies produced by the rear loudspeaker system interfere with the sound produced by the front loudspeaker system thereby causing a form of distortion. In order to place the front and rear loudspeaker systems in the same enclosure without producing such distortion, lower frequency sound energy must be eliminated from the rear loudspeaker system. The wavelength of the cut-off frequency for the appropriate high-pass filter should not generally exceed two times the smallest dimension of the baffle board on which the rear loudspeaker system is mounted.